The object of the present invention is an apparatus and method for controlling the weight of fabric produced by a textile machine, in particular by a circular textile machine.
As is known, textile machines, and in particular circular knitting machines for manufacturing knitted fabrics, are generally provided with a pick-up unit for the produced fabric piece, said unit being equipped, beyond with suitable traction rolls, with a winding roll in case the piece is picked up in rolls, or with a cloth folder in case said piece is picked up in laps.
In the case of circular knitted machines the pick-up unit consists of a structure turning integrally with the cylinder or needle bed placed above it together with the stretching rolls positioned upstream from said pick-up unit. The rotary motion of the stretching and pick-up unit and of the needle bed usually consists of a mechanical unit or, in more recent times, said motion is driven by an electric motor enslaved in its turn with an electronic unit controlling the correct working of every portion of the textile machine.
Since all the fabric pieces, either folded into rolls or piled up in laps, coming out of a knitting mill and successively sent to other departments or factories for finishing or dyeing operations must be assigned their effective weight, it is provided in the prior art to weigh each individual piece in a suitable weighing department.
In practice, some pieces produced by a given textile machine are piled up beside said machine and then periodically picked up and conveyed together with other groups of pieces coming from other machines to the weighing department, in which the weight of each piece is written down directly onto an edge of the fabric or on a card which should obviously be attached to the weighed piece.
Moreover, the weight of each piece should then be written down onto a summary form.
The weighing process briefly described above shows a number of disadvantages.
First of all, pieces have weights which can strongly vary with respect to the foreseen values, since the evaluation of the weight of a given piece during its production is generally carried out on the basis of the number of revolutions made by the knitting machine during its manufacture. According to the moisture degree, to the kind of yarn and to the knitted structure, highly different weights having the same number of revolutions and sometimes even going beyond the admissible tolerance field can correspond.
In addition, technical times directly required for the detection of the weight of fabric pieces and times required for their conveyance to the weighing departments are quite long.
The specific personnel is therefore partially diverted from carrying out more specifically manufacturing operations connected with the working of textile machines.
It should be observed that the conveyance and storing in the same place of several pieces coming from different machines can easily involve an exchange between similar pieces assigning to them features, such as the kind of yarn and the batch of raw materials used, which do not correspond to the actual features, thus clearly creating problems in the handling of the produced fabrics.
It should eventually be pointed out that the practice to put an indelible mark directly onto an edge of the fabric, which cannot therefore be used, can involve high economic losses in the case of valuable textile fibers.
In this situation the technical purpose of the present invention is to provide an apparatus and a method for controlling the weight of fabric produced by a textile machine which can substantially overcome the above-mentioned disadvantages.
Within said technical purpose an important aim of the invention is to provide an apparatus and a method allowing to obtain at the output of the textile machines wound or folded fabric pieces showing—with an extremely reduced tolerance field—a pre-established weight, independently from the kind of yarn, and therefore to reach for Instance high degrees of homogeneity of the unfinished products which should then undergo finishing or dyeing operations. Another important aim of the invention is to provide an apparatus and a method allowing to assign with certainty to every piece of manufactured fabric not only its actual weight, but also every other information which could be useful to distinguish it, such as the kind of yarn, the presence of possible defects due to machine stops, and the moisture degree at which the fabric-building process took place, thus avoiding information exchanges among the various fabric pieces due to operators' faults or other reasons.